This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Work at the BRC was conducted by David Mason a graduate student of the laboratory of Dr. Sergio Grinstein from the Hospital For Sick Children in Toronto, for three weeks during January of 2008. The broad aim of the project was to investigate new tools and methods for studying the role and importance of the Sodium / Proton Exchange (NHE) family of proteins. The model system utilised was the AP1 cell line which is devoid of the three major family members (NHE1, 2 and 3) . By individually expressing NHE isoforms of the three major types, as well as the less well characterised proteins (NHE family members now number ten ) the activity (and potentially regulation) of individual proteins could be elucidated. Electrophysiological investigation of NHE activity has historically been fraught with problems due to the electro-neutral antiport of protons for sodium. Using the SERIS technology and expertise of the resident scientists at the BRC we began to characterise the constituitive and later stimulated activity of the 'housekeeping'isoform NHE1 using both proton and to a lesser extent sodium electrodes. Basal readings were taken and a robust constituitive efflux of protons was seen in unstimulated cells. Upon release from an acid load, which causes the stimulation of NHEs , no detectable increase in proton efflux (or indeed sodium influx) was observed. Further work would investiagte the source and magnitude of the observed proton efflux potentially using mitochondrial poisons to abate metabolic proton production. Selective inhibitors of NHE isoforms could also be used to better understand isoform specific involvement in basal pH regulation.